Reinforcing and prestressing cable

ABSTRACT

A tension cable essentially composed of a multiplicity of thin strips is clamped at one or more locations with freedom of slight relative slippage of the strips to equalize their stresses. At each clamping point the strips may be separated by interposed foils which may be constituted by parts of the strips of a similar cable or by the opposite ends of the same cable bent back upon itself. The clamping pressure may be partly absorbed by laterally projecting foil portions with interposed spacers having substantially the thickness of the strips. A terminal member embraced by an end of the cable may contribute to the clamping effect.

United States Patent Puyo et al. I [45] Oct, 31, 1972 [54] REINFORCINGAND PRESTRESSING 2,941,394 6/1960 Brandt ..287/65 X CABLE 3,099,1097/1963 Hahn ..52/223 L 72 I t Andre Pu Pie Andre H 3,249,374 5/1966Muehe et al ..287/76 1 both i -Q 3,379,463 4/1968 Marshall et al...287/63 [73] Assignee: Coyne et Bellier, bureau dInprimary Examine,.Andrew V. Kundrat gemeurs Consells, Pans, France Attorney Kafl E Ross[22] Filed: Nov. 21, 1969 21 Appl. No.2 878,856 [57] ABSIMCT A tensioncable essentially composed of a multiplicity of thin strips is clampedat one or more locations with [30] Fm'gn Appliumon Pnomy Data freedom ofslight relative slippage of the strips to Nov. 26, 1968 France..68175335 equalize their stresses. At each clamping point the stripsmay be separated by interposed foils which may 1.8. CI. "287/78, beconstituted parts of the trips of a cable ..Fl6b or the opposite ends ofthe ane cable bent back [58] Field of Search ..287/63, 64, 65, 78, 76,79; upon itself The clamping pressure may be partly 52/223 223 29/452sorbed by laterally projecting foil portions with interposed spacershaving substantially the thickness of the [5 6] 1 Rem-em C'ted strips. Aterminal member embraced by an end of the UNITED STATES PATENTS cablemay contribute to the clamping effect.

2,737,802 3/1956 Bakker ..29/452 X 7 Claims, 14 Drawing FiguresPA'TENTEDncm an SHEET 1 OF 4 Andre Puyo Pierre A. Habib Inventors.

Attorney I P'A'TENTEBumax m2 SHEET 3 BF 4 Andre Puyo Pierre A. Habib I nvenfors,

By dart jl ss Attorney I msmzomm 3.701.554

- sum Ka- BF Q Andre Puyo Pierr Habib Attorney Inv nfors.

l REINFORCING AND PRESTRESSING CABLE Our present invention relates to areinforcing and/or prestressing cable to be used, for example, inconcrete construction. I

Conventional cables subjected to mechanical stress essentially consistof a multiplicity of strands of generally circular cross-section, suchas metal wires or plastic filaments, which may be twisted for greaterstrength but whose combined cross-sectional area is far less than theoverall cross-sectional area of the cable with a consequent lowering ofthe mean tensile strength per unit area. Moreover, these strands contactone another'only at isolated points, giving rise to localized stressconcentrations. Finally, the design of terminal elements for anchoringsuch a cable to a concrete body or other associated structure iscomplicated and not alwayssatisfactory.

It is, therefore, the general object of our present invention to providean improved tension cable which avoids the inconveniences referred toabove.

A related object is to provide simple means for anchoring such a cableto a structure.

A more particular object is to provide a novel cable construction,essentially composed of a multiplicity of coextensive elements of lowindividual tensile strength, wherein means are provided for effectivelydistributing the loading stresses so as to avoid any localoverstressing.

With these and other objects in view, a tension cable according to ourinvention consists essentially of a multiplicity of juxtaposed parallelstrips or ribbons of flexible character, e.g. metallic or resinous,which are of substantially the same length and preferably but notnecessarily the same width, these strips being clamped together at oneor more locations so as to be longitudinally shiftable only to theextent permitted by their elastic deformability. These strips, each ofwhich may have a thickness of as little as 0.1 mm, thus form a stackwhich in most instances will be of square or rectangular profile andwhich therefore can be easily guided in a similarly profiled channel ofan associated structure. If a high degree of slidability is desired, thecable surface and/or the channel walls may be coated or lined with alow-friction material such as polytetrafluoroethylene (Teflon).

When the cable is clamped at severallongitudinally spaced points, therelative mobility of its strips is further restricted while the appliedtension is more evenly distributed, particularly if the clampingpressure allows for some relative slippage of the strips to enable theirrealignment under stress and to facilitate stress transfer between thesepoints. Portions of the cable near a clamped extremity thereof may alsobe passed around curved high-friction guide surfaces having a secondaryrestraining effect. Such guide surfaces may be formed, for example, by acylindrically curved anchor block embraced by the cable; alternatively,they can be constituted by the walls of an undulating or meanderingchannel.

Pursuant to a further feature of our invention, the strips are separatedat the clamping point or points by interposed foils or leaves of like ordifferent material preferably having the same order of thickness; theseinterposed foils may be the strips of a similar cable spliced to orintersecting the first cable, or the opposite above.

These and other features of our invention will be described in greaterdetail hereinafter with reference to the accompanying drawing in which:

FIG. 1 is a cross-sectional view of a cable according to the invention,taken on the line I I of FIG. 2 and showing a clamping stage;

FIG. 2 is a cross-sectional view taken on the line II II of FIG. 1;

FIG. 3 is a perspective view of an assembly similar to that shown inFIGS. 1 and 2;

FIGS. 4 and 5 are graphs illustrating the longitudinal stressdistribution in a cable according to the invention;

FIG. 6 is a cross-sectional view of a multiple clamp for a cableaccording to the invention, taken on the line VI VI of FIG. 7;

FIG. 7 is a cross-sectional view taken on the line VII VII of FIG. 6;

FIG. 8 is a perspective view of an assembly similar to that shown inFIGS. 6 and 7;

FIG. 9 is an elevational view of a cable terminal according to ourinvention;

FIG. 10 is a cross-sectional view taken on the line X X of FIG. 9;

FIG. 1 l is a view similar to FIG. 9, illustrating a modification;

FIG. 12 is another view similar to FIG. 9, illustrating a further cableterminal embodying the invention;

FIG. 13 is a cross-sectional view taken on the line XIII XIII of FIG.12; and

FIG. 14 is a cross-sectional view of a modified cable which are shown tobe of the same order of thickness as the strips, may consist of similaror dissimilar material and, in particular, could be the ends of likestrips forming part of a substantially identical cable.

The strips 1 and the foils 2 are joined together under transversepressure in a clamping device comprising a rectangular frame 3, a pairof plates 4 slidably held in the frame to serve as clamp jaws andseveral pairs of complementary wedges 5, 6 inserted between the plates 4and the frame 3. The wedges 5, 6 have the profile of right trianglesslidably contacting each other along their hypotenuse, the angle ofinclination of their contact surfaces being, of course, less than theirangle of friction.

Although several wedge pairs 5, 6 have been shown disposed side by side,a single pair may suffice particularly in the case of relatively narrowstrips. In such event the pressure plates 4, serving to distribute thestress exerted by the several wedge pairs, could be omitted.

Foils 2 could also be blade-like projections of a common terminalmember, not further illustrated, to be secured to the cable by the clamp3 6.

In FIG. 3 I have shown the strips 1 separated by foils 7 extendingtransversely to the strips and projecting laterally therefrom. Theprojecting foil portions are interleaved with coextensive spacers orpads 8 which may or may not be of the same material and which havesubstantially the same thickness as the strips coplanar therewith. Therectangular stack formed by the elements 7, 8 andby the interleavedportions of strips 1 is received in a four-sided box 9 having a bottom10 with a rectangular cutout; after the box has been slid upwardly(arrow A) to receive the stack, pressure is exerted on the outermoststrips la in the direction of arrow Band C by clamping means which may,take the form of distributing platesand wedge pieces similar to theelements 4 6 of FIGS. 1 and 2 (see also FIG. 7). This pressure is partlyabsorbed by the projecting ends of foils 7 and the associated spacers 8;the remaining pressure acts upon the strips 1, la to restrain the cableagainst longitudinal displacement by a tensile force to which it may besubjected. Other conventional pressure-exerting means, such as screws,springs or hydraulic or pneumaticv jacks, may of course be used in lieuof the wedges 5, 6.

As more particularly illustrated in FIG. 7, the wedges 5, 6 may beseparated from the stack 1, 7, 8 by a pair of distributing plates 11,similar to plates 4 in FIGS. 1 and 2, as well as a pair of elasticinserts 12 juxtaposed therewith. The inserts 12 may be, for example,undulating steel plates with vertical crests and troughs as viewed inFIG. 7; they could also be constituted by pads of rubber or otherelastomeric material.

If the clamping assembly exerts upon a strip 1 a perpendicular force N,the tensile stress T required to cause slippage of the strip is equal to2fN where f is the coefficient of friction. Thus, it is always possibleto provide a clamping pressure sufficient to restrain the strips againstslippage under any applied tension up to the breaking stress of thestrip.

Nevertheless, the strip does experience a certain elongation between itsclamp jaws whereby the tension applied to it on one side of the clampingpoint generates a progressively decreasing stress over the length of theclamped strip portion. This has been illustrated in FIG. 4 where tensionT has been plotted against length L. Over the clamped length L thestress rises substantially linearly from 0 to a maximum T whichcorresponds to the applied tension. The rising stress over the length Lis proportional to'the slip between any elemental area of the strip andthe stationary clamping surfaces.

The elongation of the strip due to this progressive slip should belimited, however, to prevent any excessive weakening of the strip atthis point. Instead of a uniform application of clamping pressurethroughout the length L therefore, we may apply the highest pressure inthe vicinity of point 0 (where the tension is smallest) and to decreasethis pressure toward the side where the tension originates. A reducedstress differential per unit of length can also be realized by extendingtheeffective clamping area. Finally, it is possible to clamp the stripassembly at several longitudinally spaced points with freedom of limitedslippage at the point or points closer to the tensioned cable terminal,such as arrangement resulting in the graph of FIG. 5. According to thatgraph, the tensile stress T first rises from 0 to a relatively low valueT, over a length L, clamped at a location remote from the origin oftension; the stress then remains constant up to the second clamping areaof length L where it rises to another intermediate value T At a thirdclamping station of effective length L the tensile stress reaches itsfinal magnitude T It will be noted that the slopes of the graph of FIG.5 are considerably lower than those of the graph of FIG. 4.

FIG. 6 illustrates a relatively compact assembly for stressing a cableaccording to the invention in the aforedescribed manner by four clampingstages. These stages are constituted by four boxes 13a, 13b, 13c, 13deach forming part of a clamping assembly of the type described abovewith reference to FIG. 7. The frame portions 9 of the several boxes abutone another while their bottoms 10 are freely penetrated by the cable,the passages through these bottoms constituting the regions of constantstress shown in FIG. 5. If the cable formed by the strips 1 is to betensioned from the left as indicated by the arrow T in FIG. 6, it willbe convenient to clamp first the box 13a in position thereon, followedby the boxes 13b, 13c and 13d. Upon the application of tension, acertain amount of slippage occurs in the three last-mentioned boxes, theultimate stress distribution being analogous to that shown in FIG. 5.With a cable passing through a channel in a rigid structure such as apipe or a concrete beam, the box 13d may be placed indirect contact withsuch structure to anchor the cable to it and to hold the clampingassembly in position-The number of boxes may, of course, be increased orreduced at will.

In F IG. 8 we have shown another assembly which can be substituted, withsimilar effect, for the set of juxtaposed boxes shown in FIG. 6. Theclamping device of- FIG. 8 comprises a casing 15 with two sidewalls 15'formed along their confronting surfaces with transverse ribs 16. Therecesses between these ribs accommodate the ends of foils 7, similar tothose shown in FIGS. 3 and 7, together with the spacers 8 (not seen inFIG. 8) interleaved therewith. The sidewalls 15' may be interconnectedat the bottom of the casing, although the latter could also be open atboth ends; the longitudinal edges of these sidewalls are formed withthreaded bores 17 designed to receive bolts 19 which pass throughcorresponding holes in a series of alternately wider and narrowerbrackets 18, 20. The bolts 19 passing through brackets 18 are engaged bynuts 19' holding these brackets under pressure against the stack ofelements 1, 7, 8 within the casing; this pressure may be initiallygenerated by the nuts themselves or may have been applied by a jack orthe like, subsequently removed, with the nuts serving only as retainingelements. The brackets 18, 20 are U-shaped and embrace the housing walls15' by their arms 18a, 20a. The package I, 7, 8

lodged between any two pairs of ribs 16 confronts one of the widerbrackets 18 for individual adjustment of the pressure exerted thereon;the narrower brackets 20, aligned with the ribs 16, bear uponintermediate zones of the cable where the spacers 8 are omitted andwhere the foils 7 are foreshortened or absent; these brackets,accordingly, serve only to form a rigid connection between the wallmembers .The housing wall 15" opposite brackets 18, may be rigid withsidewalls 15' or may be secured thereto by screws similar to bolts 19and nuts 19; in either case, this wall 15" constitutes a second clampjaw cooperating with the jaws 18 of the several juxtaposed clampingassemblies. Naturally, this wall could also be subdivided intoindividual brackets 18, 20 to help select the optimum clamping pressurefor each stage.

As in the embodiment of FIG. 7, resilient means may again be providedfor elastically applying the clamp jaws against the cable strips. Thus,we. may insert compression springs such as Belleville washers 19"between the nuts 19 and the brackets 18 so that, with the bolts 19effectively connected to the remote jaw 15'', the two jaws areelastically biases toward each other.

FIGS. 9 and 10 illustrate the distribution of the stresses of severalclamping stages over a curved surface whose frictional engagement withthe cable affords a still more gradual transition between points ofmaximum and minimum stress. A terminal member or head 22 has a generallycylindrically convex peripheral surface embraced from one side by oneset of strips 1A and from the other side by another set of strips 18whose ends are interleaved with those of strips lA over a substantialpart of that curved surface. The several clamping stages are constitutedby pairs of flat bars 24 that are pivoted to head 22 by pins 23 andcarry bolts 25 traversing pressure plates 26 which are held in positionby nuts 27. Elastic pads 26a are shown interposed between the plates 26and the stack of strips 1A, 13. It will be noted that the radius ofcurvature of head 22 progressively increases from an apex, enveloped byboth groups of strips 1A, 18, to the transverse bottom edge of the headwhere its periphery flattens out. The two sets of strips 1A, 18 could bepart of a single cable bent back upon itself.

As shown in FIG. 11, the two sets of strips 1A, 1B may be combined in achannel 29 of an extension 28 of a modified head 22a, this channel beingflared so as to converge in a direction away from head 220. In thisembodiment, the head 22a is curved over an arc substantially greaterthan 180 and is studded over substantially its entire periphery byclamping stages 23 27 as described above. Member 28 may be a blockintegral with or otherwise secured to head 22a.

As shown in FIGS. 12 and 13, the strips 1 of a cable according to ourinvention may be split into two groups hugging opposite walls of anundulating channel 32 formed in a block 30. These walls are ofsinusoidal shape and form constrictions 36, 37, 38 separated by widerpassages accommodating cylindrical inserts 33, between the two cablehalves. Block 30 may consist of several laminations or sections heldtogether by transverse bolts 31. A pair of clamp jaws co-operate with aninterposed wedge 39 to engage the free ends of the two cable halves;jaws 40 may be cemented or otherwise secured to the block and are shownexternally reinforced by a fiat coil 41 of metal or the like encased ina ellipsoidal shell 42.

Advantageously, the insert 35 proximal to the clamp 39, 40 is fixedlymounted between the lateral walls 34 of channel 32 whereas the moreremote insert 33 is freely movable between these walls, thereby allowinggreater freedom of slippage to the cable portions engaged by it. The twostrip assemblies alternatively curve about the bends of the channelwalls and the in-' serts, contacting them along arcs a, B, I", y, and 8.Thus, the total surface frictionally engaged by the cable strips equalsthe sum of the arcs (oz-+- +1 +'y+8) The terminal members shown in FIGS.9 12 may again be placed directly in contact with a structure againstwhich the cable is to be stressed.

If the channel or bore to be traversed by the cable is of round ratherthan square or rectangular cross-section, the width of the strips may bestaggered to conform to its outline. This has been shown in FIG. 14

where strips 101, of like thickness but different widths,

are interleaved with foils 107 and spacers 108 complementing them'to aprismatic stack which can again be compressed in, say, a clamping box ofthe type illustrated in 3, 6, 7. Beyond the stack, the cable constitutedby the foils 101 is of generally cylindrical configuration so as to beeasily guided in a round bore of corresponding diameter.

Thus, whether the profile of the cable be round or polygonal, itscross-sectional area can always be substantially fully occupied bytensionable elements for maximum tensile strength.

We claim:

1. A cable junction comprising:

a first cable portion and a second cable portion each composedessentially of a multiplicity of flat, superposed and substantiallylongitudinally coextensive strips, the strips of said first cableportion having extremities interleaved with extremities of the strips ofsaid second cable portion in direct broadsurface contact throughout apredetermined zone of overlap;

a body with a curved guide surface hugged by an on termost one of saidstrips in said zone of overlap;

and a plurality of clamps engaging said strips at longitudinally spacedlocations and bearing upon said interleaved extremities under transversepressure exerted against said body.

2. A cable junction as defined in claim 1 wherein said body forms partof a terminal member and has a generally cylindrically convex surfaceembraced by a terminal portion of said strips.

3. A cable junction as defined in claim 2 wherein the strips of saidcable portions are wound about said convex surface in oppositedirections.

4. A cable junction as defined in claim 3 wherein said terminal memberhas an extension of said body formed with a channel converging in adirection away from said convex surface, said strips passing throughsaid channel and merging therein into a single cable.

5. A cable junction comprising:

a first cable portion and a second cable portion each composedessentially of a multiplicity of flat, superposed and substantiallylongitudinally coextensive strips, the strips of said first cableportion having extremities interleaved with extremities of the strips ofsaid second cable portion in direct broadsurface contact throughout apredetermined zone of overlap;

and resilient clamping means yieldably bearing upon said interleavedextremities under transverse pressure over part of said zone, saidclamping means comprising a pair of jaws and at least one elastic insertbetween said jaws and said strips.

6; A cable junction comprising:

a cable bent back upon itself and composed essentially of a multiplicityof flat, superposed and substantially longitudinally coextensivestripswith opposite extremities interleaved in direct broad-surfacecontact throughout a predetermined zone of overlap;

and clamping means bearing upon said interleaved extremities undertransverse pressure over part. of said zone.

7. A cable junction comprising:

a first cable portion and a second cable portion each composedessentially of a multiplicity of flat, su-

perposed and substantially longitudinally coextensive strips, the stripsof said first cable portion having extremities interleaved withextremities of the strips of said second cable portion in directbroadsurface contact throughout a predetermined zone of overlap;

and clamping means bearing upon said interleaved extremities undertransverse pressure over part of said zone, said strips being engaged bysaid clamping means with freedom of slight relative slippage, saidclamping means comprising a plurality of clamps engaging said strips atlongitudinally spaced locations and a body with a curved guide surfacein frictional engagement with an outermost one of said strips at aplurality of locations over a length of cable hugging said surface.

* III UNITED STATES PATENT OFFICE (IERTIFICATE ()F CORRECTION PATENT NO.3,701,554 DATED 31 October 1972 INVENTOR(S) Andr PUYO and Pierre AndreHABIB It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

In the heading, line F37, after the situs of the Assignee, reed:

-- Assignee of one half (50%) and Pierre Andr HABIB,

Paris, FRANCE, Assignee of one half (50%) Signed and Scaled thisnineleenflz Day Of August 1975 [SEAL] A ttest:

RUTH C MASON C. MARSHALL DANN X QUIT? ('mnmissinncr ufPatenIs andTrademurkx

1. A cable junction comprising: a first cable portion and a second cable portion each composed essentially of a multiplicity of flat, sUperposed and substantially longitudinally coextensive strips, the strips of said first cable portion having extremities interleaved with extremities of the strips of said second cable portion in direct broad-surface contact throughout a predetermined zone of overlap; a body with a curved guide surface hugged by an outermost one of said strips in said zone of overlap; and a plurality of clamps engaging said strips at longitudinally spaced locations and bearing upon said interleaved extremities under transverse pressure exerted against said body.
 2. A cable junction as defined in claim 1 wherein said body forms part of a terminal member and has a generally cylindrically convex surface embraced by a terminal portion of said strips.
 3. A cable junction as defined in claim 2 wherein the strips of said cable portions are wound about said convex surface in opposite directions.
 4. A cable junction as defined in claim 3 wherein said terminal member has an extension of said body formed with a channel converging in a direction away from said convex surface, said strips passing through said channel and merging therein into a single cable.
 5. A cable junction comprising: a first cable portion and a second cable portion each composed essentially of a multiplicity of flat, superposed and substantially longitudinally coextensive strips, the strips of said first cable portion having extremities interleaved with extremities of the strips of said second cable portion in direct broad-surface contact throughout a predetermined zone of overlap; and resilient clamping means yieldably bearing upon said interleaved extremities under transverse pressure over part of said zone, said clamping means comprising a pair of jaws and at least one elastic insert between said jaws and said strips.
 6. A cable junction comprising: a cable bent back upon itself and composed essentially of a multiplicity of flat, superposed and substantially longitudinally coextensive strips with opposite extremities interleaved in direct broad-surface contact throughout a predetermined zone of overlap; and clamping means bearing upon said interleaved extremities under transverse pressure over part of said zone.
 7. A cable junction comprising: a first cable portion and a second cable portion each composed essentially of a multiplicity of flat, superposed and substantially longitudinally coextensive strips, the strips of said first cable portion having extremities interleaved with extremities of the strips of said second cable portion in direct broad-surface contact throughout a predetermined zone of overlap; and clamping means bearing upon said interleaved extremities under transverse pressure over part of said zone, said strips being engaged by said clamping means with freedom of slight relative slippage, said clamping means comprising a plurality of clamps engaging said strips at longitudinally spaced locations and a body with a curved guide surface in frictional engagement with an outermost one of said strips at a plurality of locations over a length of cable hugging said surface. 